I've always been amused that the American comedian and actor, Albert Brooks, had to change his real name. He just couldn't see himself using his real name -- Albert Einstein. (His brother, who played the idiot character Super Dave back in the 80s, kept his real name, performing under the name Bob Einstein.)

-the other Doug

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“The trouble ain't that there is too many fools, but that the lightning ain't distributed right.” -Mark Twain

There's some more on it over on the planetary society blog. Thanks Emily! The description of how water adsorption works is excellent, it really clarifies the difference between thin films of water and thin films of liquid water.

Looks like there is someone defending that the droplets seen on Phoenix's legs are made out of...liquid water... "Nilton Renno from the University of Michigan and Phoenix team member, thinks it could be. "According to my calculations, you can have liquid saline solutions just below the surface almost anywhere on Mars," he said."Story at Universetoday.

Very interesting abstract. I'm hanging out to hear the full exposition at the conference. This is an important topic with wide implications. Well, they say they have a smoking gun, and let's hope it doesn't turn out to be the smoky sublimation from an ice pistol (sorry I couldn't resist!).

This is basically the story of the photos of two spheroids on the legs of Phoenix. From these photos it looks like a smaller spheroid could have merged with a larger one just below it. For a really good enhanced photo - by HortonHeardAWho - of Phoenix leg and spheroids go to http://www.flickr.com/photos/hortonheardaw...392520/sizes/o/

From my amateur level of understanding the key underpinning general points are that: -a. The index of refraction of liquid water is larger than that of water ice. [Thus - in these photos - a darker spheroid is likely to be liquid.]b. If the spheroids were made up of supersaturated aqueous solutions they would grow due to attracting atmospheric water vapour hygroscopically (deliquescence). c. If they were made up of ice, they would sublimate and so would shrink. [Counter argument: Alternative explanation for growth - water vapour from ice below Phoenix could have sublimated and recondensed on ice spheroids on the relatively cold (in shadow) legs faster than the spheroids were sublimating].

However, the spheroids are highly like to be liquid as: -1. The fact that shapes observed were spheroidal suggests the presence of the liquid phase. (They could have gone through a number of freeze/thaw cycles).2. The small upper spheroid darkened between photos. This suggests it changed phase from ice to liquid.3. The spheroids look as if they joined between photos with the upper spheroid reduced in size afterwards (actual joining not observed). Thus they moved. Therefore they were liquid. [Counter argument - changing light between photos only gives the illusion of movement.]4. Growth is suppressed in the smaller upper spheroid left behind.......suggesting that when it moved most of its salts were carried with it. [Implication - as a less concentrated solution it froze. This runs against the counter argument in a. above which indicates it should have grown].

4. Growth is suppressed in the smaller upper spheroid left behind.......suggesting that when it moved most of its salts were carried with it.

The growth rate suppression is the part I don't quite get.

In the scenario where the two spheroids merged, as the two spheroids joined, the capillary action should have sucked the bulk of the initial upper drop into the lower drop. The uppermost part of the drop would have clung (hanging on for dear life) to the surface of the strut.

The initial upper drop salt concentration should have been uniform across the drop. So when it got ripped apart, the salt concentration in the remaining part of the upper drop should have been the exact same as the part of the upper drop that joined the lower drop.

I *think* that assuming an equilibrium, the salt concentrations of all the drops should all be the same. So the size of the drop should only be dependent on the amount of initial salt that nucleated the deliquesence.

So after the merge/ripping apart, the small remaining upper drop will have a smaller absolute quantity of salt than the big lower merged drop. (The concentration of the two drops should be the same).

If at the time of merge/ripping apart all the drops were close to the maximal final concentration, then the growth rates for all the drops would be pretty small.

So after the merge, did all the drops grow faster than the remainder upper drop? Or were all the growth rates similar (if at all, the merge could have happened close to maximal drop size)

-Mike

[EDIT: Using the images in the abstract, it looks most of the neighbor drops increased ca. 10% from Sol 31 to Sol 44, but the remainder drop didn't appear to increase. I'm baffled.]

Oh wait! I get it! Here's a possible mechanism for shrinkage of the remainder:

If the drop was cooling before it merged, then ice would have been crystallizing out of the solution! (refer to simplified phase diagram Fig 1 in abstract)

The drop would thus be non-uniform, a mixture of solid precipitated ice and salts in solution. I'd assume that the ice crystals would nucleate and form at the surface imperfection of the lander strut. So at the time of merge, the salt solution would be pulled over to the big drop, but most of the ice crystals would stay behind with the remainder.

So at the instant of the merge, the salt concentrations of the remainder and merged drops would be the same.

But after warming, and melting of the upper remainder's ice crystals, the salt concentration would be too dilute! Thus water could evaporate off the upper remainder drop until the preferred equilibrium concentration was reached. The remainder drop would shrink!

-Mike

[Now if I understand this right, it should also be possible to imagine a scenario/conditions where salts would have been precipitating at the time of merge. This would cause a remaining drop to grow faster than expected.]

If this really is liquid water, it would be a tremendous discovery. It seems a pretty hard conclusion to draw from three* monochrome and fairly low resolution images, with theorizing alone to back up the interpretation. I would really like to see laboratory replication of all of the lines of evidence that it is suggested that we observe in these images. For starters, what should be a pretty easy experiment: prepare a candidate perchlorate brine solution and a controlled experiment box which can replicate the temperature and pressure of the martian pole. Spray the brine on a metal pipe and take photographs under various lighting conditions. Compare with the images from Phoenix. Can you make spherules which look the same? Show clearly how to distinguish between lighting changes and motion and growth/shrinkage of droplets. Try doing the same thing with frozen droplets. Is there something that distinguishes the liquid from the frozen droplets in a still photograph? For a more advanced test, try to demonstrate the effects claimed as "smoking gun" signs in Renno et. al.'s abstract: if temperature, pressure, and humidity are varied over a cycle consistent what was observed by Phoenix, droplet growth is suppressed on material left behind by a droplet that merges with a neighbor; droplets grow selectively where the pipe is splashed with perchlorate salts; and their sizes and growth is proportional to their volume.

I'm really excited about the possibility of liquid water on mars today, but extraordinary claims require extraordinary evidence. So far this looks more at the level of (highly educated) speculation than an airtight demonstration of fact.

(*can any of the image guru's tell me if there really are only 3 images of that strut? Or are there more that just weren't selected for the comparison, because lighting conditions differ or something?)

A couple of very good points were made over on the baut forum, Phoenix Mars Results thread that warrant repeating here.

In the few seconds of the landing cycle the environment under the lander was high temperature (1200k) and high pressure Ammonia/Nitrogen from the exhaust. This temperature would have broken down perchlorates and vaporised part of the ice layer. Water vapour and dust mixed with the extremely hydroscopic ammonia provides for some interesting products. We can have no certainty over what the the deposits on the strut are made up of, but a possible ammonia water solution, concentration unknown makes for some interesting possibilities.

But the key point made is that the deposits are an exotic phenomenon attributable to the lander - not the Martian environment, and have no relevance to the Martian environment..

Upcoming Lunar and Planetary Science Conference abstracts can be sourced from here http://www.lpi.usra.edu/meetings/lpsc2009/pdf/program.pdf - Interesting looking papers - March 23 Phoenix: Exploration of the Martian Arctic - also - Phoenix: Soil, Chemistry and Habitability. Lots of poster sessions on Mars and other interesting stuff. Is any of this going to be put out as a webcast?

What has irked me is that the media, and even specialist (should-know-better) media have been pushing this as 'liquid water found on Mars'.

No it wasn't.

It was found on Phoenix. Several hundred pounds of metal and wires that expended most of its energy budget keeping itself warm, having blasted the surface with >1kdegC thruster exhausts. Those droplets tell us very very little about Mars. They tell us about Phoenix.

It shows that at least under special surface conditions, atmospheric water can condense (deliquese) onto exposed residual salts.

Can those special conditions also exist naturally on Mars?How abundant? (thermal inertia of substrata?, regional salt types with similar chemical properties?)How often? (seasonal?, certain times of day?)

The most similar natural phenomenon to the landing could be the small meteor impacts.

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"I can easily see still in my mind’s-eye the beautiful clusters of these berries as they appeared to me..., when I came upon an undiscovered bed of them... – the rich clusters drooping in the shade there and bluing all the ground" -- Thoreau

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